1. Field of the Invention
The invention relates to a toothbrush having a one-piece, plastic injection moulded brush body comprising a substantially rigid head receiving the bristles, a substantially rigid handle and a tapering neck connecting said two parts, which has a spring part made from a material with a higher modulus of elasticity than the plastic of the brush body.
2. Description of the Prior Art
Toothbrushes are mainly used for cleaning the teeth and the interdental gaps, but frequently also are used to exercise a massaging action on the gums or the marginal areas thereof. The latter action has more particularly led to special constructional measures on toothbrushes. These include the construction of a resilient connection between the brush head and the handle, because, for stability reasons, they are made from a comparatively rigid plastic, generally by injection molding.
Various constructions are known for obtaining a resilient connection between the brush head and the handle. According to FR 1 247 433 the head is xe2x80x9csplitxe2x80x9d longitudinally down to the handle area and the ledge-like parts covered with bristles are overengaged by a locking ring, by means of which the free length of the ledges and consequently the flexibility of this more elastic area than the handle can be adjusted. This construction is complicated from the design and use standpoints. Due to the gaps which exist it is subject to hygienic objections. Much the same applies for another construction (U.S. Pat. No. 4,520,526), in which the toothbrush is weakened in the transition area between the head and the handle by recesses in the plastic, so as to give said area a greater resilience. Here again dirt, toothpaste residues, bacteria, etc. can be deposited. Much the same applies for constructions in which the transition area is provided with pronounced profilings (EP 0 281 017, WO 93/15 627).
Therefore from the hygienic standpoint preference is given to those constructions in which the transition between the brush head and the handle is of a substantially smooth-walled nature, although a spring action is obtained. Thus, it is known (DE 38 40 136) to insert a metal leaf spring in the transition area between the handle and the brush head and to embed said spring completely in the plastic. With the leaf spring, which has a higher modulus of elasticity than the plastic surrounding it, it is possible to ensure a moving back of the toothbrush in the case of excessive pressure, as well as a constant, adequate pressure application when the toothbrush is correctly guided.
Even though this construction with a metallic leaf spring is largely satisfactory from the use standpoint, it still suffers from a number of disadvantages. It leads to the manufacturing problem that the leaf spring must be injection moulded into the plastic, which requires corresponding constructional precautions on the injection mould. In addition, due to their extremely thin wall thickness leaf springs during the manufacturing sequence are difficult to handle both manually and with manipulators and can only be positioned with difficulty in the injection moulding machine. They also form no connection with the surrounding plastic. Thus, on springing out in the vicinity of the edges of the leaf spring necessarily compressive and shear stresses act on the surrounding plastic, which can lead to breaking of the cross-section in the transition area between the brush head and the handle must be overdimensioned. However, particularly at this point an especially slender shape is desired, so that it is possible to guide the necessary movements of the toothbrush even with the mouth closed. Finally, all metallic materials are undesired in the oral hygiene sector, even if as in the present case they are not exposed. They also represent a substantial problem during the recycling of toothbrushes, which has considerable importance due to the mass consumption thereof. A complete separation of the materials would require a complete crushing of the toothbrush. In view of the small weight proportion of the metal the costs involved would hardly be acceptable.
Finally, it has already been proposed (WO 93/15 627, DE 38 40 136) to make the brush body extremely slender in the vicinity of the neck and in this way obtain a spring action. A rubber-elastic elastomer is then injected around the very thin cross-section. The plastics normally used for the brush body do not have an adequate modulus of elasticity, in order to obtain an adequate and in particular permanent spring action. In addition, the transitions from the handle or head must be extremely steep, so that at the transitions breakages can easily occur. If an adequately high modulus of elasticity is provided, then very high-grade plastics must be used for the brush body. This is unacceptable from the costs standpoint with mass produced articles, like toothbrushes.
The invention is a toothbrush, which is simple to manufacture, favourable to use and also environmentally friendly. It must also be possible to easily adjust the spring action.
According to the invention this problem is solved by the spring part, with the higher modulus of elasticity than the plastic of the brush body, being at least preponderantly made from plastic and is at least partly embedded in the plastic of the brush body, accompanied by the formation of the neck. Instead of this, the spring part can also at least partly envelop the brush body in the neck area.
The invention firstly leads to the advantage that the toothbrush is entirely made from plastic and consequently no disposal problems occur. In addition, any metal fraction, which is undesired in the oral hygiene sector, is avoided. Finally, such a toothbrush can be inexpensively manufactured, e.g. in two-component injection moulding processes, embedding processes, etc. As the plastic spring part is embedded in plastic, there is no alien material pairing and as a function of the plastics there can even be an integral joint. Only the spring part need be made from high-grade plastic, whereas the brush body can be made from conventional, inexpensive plastics.
The spring part can be made exclusively of pure or a filled plastic, the fillers being present in a proportion of 1 to 30 vol. %.
Preferably the spring part is made from a fiber-reinforced plastic, use being preferably made of glass fibers. Such a spring part can be separately injection molded and then inserted or injection mould in integrated manner in the injection mould for the toothbrush. However, the spring part can also be produced by injection moulding round the neck area of the brush body.
The spring part can have a flat, polygonal, round or oval cross-section, but also a U, T or I-cross-section, so as in this way to influence the nature of the springing out of the brush head. This springing out can not only be provided counter to the pressure on the tooth surface, but also at least to a limited extent transversely thereto or in any random direction.
Advantageously the spring part has a higher moment in inertia than the remaining neck cross-section and extends substantially over the entire brush body neck length.
The construction according to the invention gives the possibility of adjusting the spring tension of the spring part through the choice of the plastic and/or the fillers and/or its cross-section. This spring tension adjustment can take place within wide ranges. Thus, for toothbrushes for children a smaller resilience is used than for toothbrushes for adults. Compared with all known constructions there is a material and consequently cost saving. The neck can also be made extremely slender with gentle transitions between the handle and the head.
In a further preferred construction the spring part has projections transversely to its extension. These projections can initially serve as simple positioning aids in the injection mould and also for maintaining position during moulding. In addition, the spring part is xe2x80x9ccenteredxe2x80x9d and anchored in the surrounding plastic mass.
The invention more particularly offers the possibility for the projections to extend up to the surface of the plastic enveloping the spring part. This also leads to the manufacturing advantage that the spring part can be positioned directly at the mould wall and no position aids have to extend into the cavity. These projections are not prejudicial on the surface, because they are also made from plastic.
In the area on which they appear on the visible side, said projections can in fact fulfil a further function, namely as information carriers, e.g. for manufacturers"" marks, publicity slogans, use information, etc. and can be shaped as such.
In a further advantageous construction the spring part with its elongated surfaces is located on the surface of the enveloping plastic.
This simultaneously provides a large-surface support of the spring part in the injection mold for the handle and head of the toothbrush. In particular the spring part with said elongated surface on the one hand and the projections located on the opposite side on the other can be fixed between the two injection mold parts and therefore accurately positioned. By a corresponding colouring of the spring part, its spring function can be optically indicated.
According to another advantageous embodiment, in the gripping area of the handle is embedded at least one gripping element made from a plastic with a higher friction coefficient than that of the surrounding plastic.
For optical and hygienic reasons the handle and head of a plastic toothbrush are generally made from a plastic with a smooth and optionally glossy surface, so that the hand is not subject to particularly good handling characteristics and is not grip-proof. This disadvantage is increased by the spring characteristic in the vicinity of the brush neck, because the head performs relative movements with respect to the handle and consequently the hold of the fingers on the handle is reduced and the fingers can easily slip off. This is counteracted by the gripping elements with increased friction coefficients. They ensure that the fingers have a firm hold on the handle, so that the toothbrush does not slip when used.
Preferably the gripping element is made from an elastomer, which inherently has a higher friction coefficient than the thermoplastics normally used for the head and handle.
The good grip can be further increased in that in each case one gripping element is provided on the top and bottom of the handle, so that the thumb gripping the underside also has a firm hold.
A further improvement to the good handle action results from the fact that the gripping elements are provided on their exposed surface with a friction increasing profile, which e.g. follows the shape of the finger tips.
The two gripping elements on the top and bottom are preferably in contact in the interior of the handle, which facilitates their insertion in the injection mould. However, they can also pass into one another in one piece. In conjunction with the construction of the gripping elements from an elastomer, a very elastic gripping surface is obtained.
Finally, the spring part and the gripping elements are preshaped and injected round by the plastic forming the handle and head.
In place of a separate production of the parts and subsequent embedding or injecting round, it is also possible to produce the brush body, spring part and gripping elements in a multicomponent injection moulding process.